Abstract
Over the past 20 years, there has been a consistently high prevalence of urogenital carcinoma in California sea lions (Zalophus californianus) along the west coast of the US1-3. Primary tumors form in the vagina, cervix or penis, and aggressively metastasize throughout the body, resulting in stranding or death2. Contaminants, genetic predisposition and a virus, otarine herpesvirus 1 (OtHV1), have all been associated with this cancer, however the etiology is not fully understood4-7. For example, OtHV1 has been detected in genital swabs from animals with and without urogenital carcinoma, making it unclear if this virus is causative or a consequence, of this cancer7. Here we explore the role of OtHV1 by examining the viral genome and gene expression patterns in cervix tissue from sea lions with and without urogenital carcinoma.
Next generation sequencing (MiSeq) was used to generate the OtHV1 genome from a sea lion cervical tumor. The viral genome was annotated and compared to those of herpesviruses that cause cancer in humans (Kaposi’s sarcoma herpesvirus and Epstein Barr herpesvirus). Within the OtHV1 genome, several herpesvirus gene homologues known to induce cancer were identified. Next, RNA in situ hybridization probes (BaseScope) were designed to bind to suspected viral oncogene mRNA to determine whether these were actively expressed in cancer tissue and/or in healthy sea lion cervix. Five OtHV1 genes of interest were assessed in nine normal cervices and 16 cervices with urogenital carcinoma.
In sea lions without cancer, no expression of OtHV1 genes was seen in normal cervical epithelium. However, in sea lions with urogenital carcinoma, there was very high expression of all OtHV1 genes examined within the carcinoma cells of the cervical epithelium. This indicates that OtHV1 expression is associated with tumor tissue and not normal cervical epithelium.
The homologous viral oncogenes, and localization of viral expression in cervical urogenital carcinoma cells, strongly support the hypothesis that OtHV1 plays a significant role in the development of this persistently common cancer observed in California sea lions. Like herpesvirus-induced cancer in humans, it is likely that a variety of influences are affecting the pathogenicity of herpesvirus during the development of urogenital carcinoma. Future research on the effects of contaminant exposure and genetic predisposition on the behavior of OtHV1 may provide important insight into how virally induced cancers are perpetuated in sea lions as well as other mammalian species.
Acknowledgements
The study was funded by the Geoffrey Hughes Research Fellowship and The Marine Mammal Center. We thank the dedicated staff and volunteers at The Marine Mammal Center for the care provided to all animals. Particular thanks to Cara Field, Barbie Halaska, Christine Fontaine, Tenaya Norris, Lauren Rust, Erin Brodie, and Liz Wheeler for assisting with necropsies and tissue sampling. This study was permitted by the National Marine Fisheries Service Marine Mammal Protection Act permit number 18786 and the Institutional Animal Care and Use Committees of the University of Florida (no. 201608188) and the Marine Mammal Center (2014-1).
* Presenting author
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